| Title | Cephalosporin MIC distribution of ESBL and pAmpC producing Escherichia coli and Klebsiella species. | | Author(s) | Kohner PC, Robberts FJ, Cockerill FR, Patel R | | Institution | Division of Clinical Microbiology, Department of Laboratory Medicine and Pathology, Division of Infectious Diseases, Department of Medicine, Mayo Clinic Rochester, Minnesota. | | Source | J Clin Microbiol 2009 Jun 3. | | Abstract | Acquired beta-lactamases in Enterobacteriaceae pose a challenge to antimicrobial susceptibility testing in the clinical laboratory. We correlated the MIC distribution of Klebsiella spp. and Escherichia coli with the presence of extended-spectrum beta-lactamase (ESBL) and AmpC beta-lactamase (pAmpC) genes. 264 isolates were subjected to cefazolin, ceftriaxone, cefotaxime, ceftazidime, cefepime and aztreonam agar dilution MIC determination, Clinical and Laboratory Standards Institute (CLSI) ESBL screen/confirmatory testing, and (for isolates displaying an MIC >/=1 microg/ml toward a third generation cephalosporin or >4 microg/ml toward cefpodoxime), PCR amplification and sequencing of ESBL and pAmpC genes. PCR was positive in 73/81 isolates (45 with ESBL and 24 with pAmpC genes alone, with both detected in 4). Compared to PCR, CLSI confirmatory testing yielded a sensitivity and specificity of 98.0 and 96.3%, respectively, with 6 false-positive and 1 false-negative results. No distinction in MIC distribution was apparent between isolates with ESBL and pAmpC genes. A substantial percentage of isolates with PCR-confirmed ESBL and/or pAmpC genes fell within the current CLSI susceptible category. At an MIC of >/= 2 microg/ml to ceftazidime, ceftriaxone, or cefotaxime, a dichotomy existed between isolates with and without ESBL/pAmpC genes, in most cases. This suggests that ESBL and pAmpC enzymes may yield similar MIC values toward extended spectrum cephalosporins, many of which fall within current non-resistant categories. Lowering current CLSI breakpoints for cephalosporins appears warranted. | | Language | ENG | | Pub Type(s) | JOURNAL ARTICLE
| | PubMed ID | 19494061 |
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